code: def on_exp_start(self):
      self.stat_aggregates.setdefault(
          "times",
          dict(
              runs=[],
              folds=[],
              reps=[],
              total_elapsed=None,
              start=None,
              end=None,
          ),
      )
      self.stat_aggregates["times"]["start"] = str(datetime.now())
      self.stat_aggregates["times"]["total_elapsed"] = datetime.now()
      super().on_exp_start()
  
imports: from hyperparameter_hunter.callbacks.bases import BaseAggregatorCallback
  from datetime import datetime
  import numpy
label_desc: Use image node_id 1 for calling the AggregatorTimes obj's underlying member method code with example usage: obj.on_exp_start() without return types